An Italian prosecutor has opened a manslaughter investigation into the deaths of British tech magnate Mike Lynch and six other people who were killed when a luxury yacht sank off Sicily this week.

The public prosecutor’s office of Termini Imerese, headed by Ambrogio Cartosio, announced the investigation, saying the probe was not aimed at any individual person.

Lynch’s 18-year-old daughter, Hannah, was also among those who died when the family’s 56-metre-long (184-foot) boat, the Bayesian, capsized during a fierce, pre-dawn storm on Monday off Porticello, near Palermo.

Fifteen people survived, including Lynch’s wife, whose company owned the Bayesian, and the yacht’s captain.

The captain, James Cutfield, and the other survivors have been questioned by the coast guard on behalf of prosecutors. None of them have commented publicly on how the ship went down.

Hannah Lynch’s body was discovered on Friday by divers who scoured the submerged vessel for the past five days. The five other dead passengers were recovered on Wednesday and Thursday, while the body of the only crew member who died, onboard chef Recaldo Thomas, was found on Monday.

The sinking has puzzled naval marine experts who say a boat like the Bayesian, built by Italian high-end yacht manufacturer Perini, should have withstood the storm and in any case should not have sunk as quickly as it did.